lingua franca

A region usually adopts a lingua franca, or common language, when its inhabitants speak many different languages or dialects.

India, a country in which people speak hundreds of different languages, chose Hindi in the 1950s to be its lingua franca so that citizens would be able to communicate with each other. The term is an Italian word meaning "Frankish tongue," a reference to the original lingua franca, a mixture of Italian, French, Turkish, and other languages in the Mediterranean region that was used between the eleventh and nineteenth centuries.

Definitions of lingua franca
1

n a common language used by speakers of different languages

“Koine is a dialect of ancient Greek that was the lingua franca of the empire of Alexander the Great and was widely spoken throughout the eastern Mediterranean area in Roman times”
Synonyms:
interlanguage, koine
Type of:
language, linguistic communication
a systematic means of communicating by the use of sounds or conventional symbols

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